Multi-core optical fiber and method for designing multi-core optical fiber

A multi-core optical fiber comprising:

• a plurality of cores that is disposed in a square lattice shape or in a line along a longitudinal direction of the multi-core optical fiber;
• a plurality of first cladding regions that surrounds the plurality of cores, respectively, and has a refractive index lower than a refractive index of the surrounded
• a plurality of second cladding regions that surrounds the plurality of first cladding regions, respectively, and has a refractive index lower than the refractive index of the surrounded first cladding regions;
• and
• a third cladding region that surrounds the plurality of second cladding regions and has a refractive index lower than the refractive index of the plurality of cores,
• wherein
• a diameter of the third cladding region is 125±1 μm,
• a cutoff wavelength is 1.53 μm or less,
• a mode field diameter of the plurality of cores at a wavelength of 1.55 μm is 9.5 μm to 15.0 μm, and
• a core interval of the plurality of cores is 33 μm to 50 μm.

A method for designing a multi-core optical fiber, the multi-core optical fiber including:

• a plurality of cores that is disposed in a square lattice shape or in a line along a longitudinal direction of the multi-core optical fiber;
• a plurality of first cladding regions that surrounds the plurality of cores, respectively, and has a refractive index lower than a refractive index of the surrounded
• a plurality of second cladding regions that surrounds the plurality of first cladding regions, respectively, and has a refractive index lower than the refractive index of the surrounded first cladding regions;
• and
• a third cladding region that surrounds the plurality of second cladding regions and has a refractive index lower than the refractive index of the plurality of cores,
• the method comprising:
• calculating, by a computer, a mode field diameter and a core interval corresponding to a region surrounded by intersections of a first line indicating an upper limit of a core interval in which an excessive loss of a core is equal to or less than a predetermined value, a second line indicating a lower limit of a core interval in which crosstalk between cores is equal to or less than a predetermined value, and a third line indicating a lower limit of a mode field diameter in which an increase amount of Rayleigh scattering loss of a core is equal to or less than a predetermined value in a graph representing a relationship between a mode field diameter and a core interval as a mode field diameter and a core interval of the plurality of cores.